Sulfuric acid plants using the contact process include packed towers for the transfer of water vapour and sulfur trioxide from carrier gases to a sulfiuric acid stream for drying of air or sulfur trioxide absorption, respectively. These towers are, generally, brick-lined and contain ceramic packing. The tower can be as large as ten meters in diameter and contain packing up to four meters deep. Typically, the height of the packing is less than the tower diameter, which can result in problems with both liquid and gas distribution. Liquid flows can be very large and range up to 2500 cubic meters per hour (10,000 U.S. gallons per minute). Gas flows can range as high as 250,000 cubic meters per hour. Tower efficiencies must be very high for the processes to work successfully.
Ceramic packing has been used in packed towers in the contact process for many years. In early plants, such shapes included quartz rocks, pipe sections (Rashig Rings), crushed bricks and special shapes, such as saddles. Most of these shapes had limited gas treatment capacities and the towers were relatively large for the production capacity. Flow restrictions caused by the acid distributors in such towers did not constrain tower capacity. Typical distributors in such towers include pan and trough units, optionally with overflow weirs while others provided downcomers, to carry the acid into the packing. Another variety of distributor contained cast iron pipes with drilled holes servicing as orifices to meter the acid into the packing.
While commercial distributors provide reasonable absorption efficacy, none provide good structural marriages of linear geometry to the circular cross-section of the typical tower. In some cases, many more distribution points have been added to generate a better tower performance, while in the majority of other cases additional packing is used. Distributors which generate more effective liquid distribution, but not necessarily uniform distribution are needed.
Specifically, prior art distributors have feed conduit layouts which generally take the form of a central feed conduit the full diameter of the distributor and extending between the walls across from which a plurality of coplanar chordal cross-member conduits perpendicularly extend. However, the cross-member conduits do not interconnect one to another and terminate adjacent the distributor wall. However, such conduit layouts do not provide fully satisfactory liquid circumferential distribution adjacent and at the distributor wall around the full inner circumference of the wall surface. No provision is made for a network constituted as a full or substantial essentially continuous loop.
Structural areas which need to be addressed are those which provide, namely, (1) distribution from a single feed line into a header system, (2) distribution from the header system to the individual feed points, and (3) distribution from the feed points to the packing.
There is, therefore, a need for a more efficient liquid distribution system, particularly, in absorption and drying towers of use in sulfuric acid manufacture.